msglist: Retrieve topic from failed-to-send messages

Fixes: zulip#1441

Author: PIG208

lib/widgets/compose_box.dart

@@ -1141,15 +1141,8 @@ class _SendButtonState extends State<_SendButton> {
     final content = controller.content.textNormalized;
 
     controller.content.clear();
-    // The following `stoppedComposing` call is currently redundant,
-    // because clearing input sends a "typing stopped" notice.
-    // It will be necessary once we resolve #720.
-    store.typingNotifier.stoppedComposing();
 
     try {
-      // TODO(#720) clear content input only on success response;
-      //   while waiting, put input(s) and send button into a disabled
-      //   "working on it" state (letting input text be selected for copying).
       await store.sendMessage(destination: widget.getDestination(), content: content);
     } on ApiRequestException catch (e) {
       if (!mounted) return;
@@ -1241,7 +1234,6 @@ class _ComposeBoxContainer extends StatelessWidget {
         border: Border(top: BorderSide(color: designVariables.borderBar)),
         boxShadow: ComposeBoxTheme.of(context).boxShadow,
       ),
-      // TODO(#720) try a Stack for the overlaid linear progress indicator
       child: Material(
         color: designVariables.composeBoxBg,
         child: Column(
@@ -1476,10 +1468,6 @@ class _ErrorBanner extends _Banner {
 
   @override
   Widget? buildTrailing(context) {
-    // TODO(#720) "x" button goes here.
-    //   24px square with 8px touchable padding in all directions?
-    //   and `bool get padEnd => false`; see Figma:
-    //     https://www.figma.com/design/1JTNtYo9memgW7vV6d0ygq/Zulip-Mobile?node-id=4031-17029&m=dev
     return null;
   }
 }
@@ -1610,11 +1598,6 @@ class _ComposeBoxState extends State<ComposeBox> with PerAccountStoreAwareStateM
       }
     }
 
-    // TODO(#720) dismissable message-send error, maybe something like:
-    //     if (controller.sendMessageError.value != null) {
-    //       errorBanner = _ErrorBanner(label:
-    //         ZulipLocalizations.of(context).errorSendMessageTimeout);
-    //     }
     return _ComposeBoxContainer(body: body, banner: null);
   }
 }

lib/widgets/message_list.dart

@@ -1516,7 +1516,6 @@ class OutboxMessageWithPossibleSender extends StatelessWidget {
 
   final MessageListOutboxMessageItem item;
 
-  // TODO should we restore the topic as well?
   void _handlePress(BuildContext context) {
     final content = item.message.content.endsWith('\n')
       ? item.message.content : '${item.message.content}\n';
@@ -1528,6 +1527,13 @@ class OutboxMessageWithPossibleSender extends StatelessWidget {
       composeBoxController.contentFocusNode.requestFocus();
     }
 
+    if (composeBoxController case StreamComposeBoxController(:final topic)) {
+      final conversation = item.message.conversation;
+      if (conversation is StreamConversation) {
+        topic.setTopic(conversation.topic);
+      }
+    }
+
     final store = PerAccountStoreWidget.of(context);
     assert(store.outboxMessages.containsKey(item.message.localMessageId));
     store.removeOutboxMessage(item.message.localMessageId);

test/widgets/message_list_test.dart

@@ -11,6 +11,7 @@ import 'package:zulip/api/model/events.dart';
 import 'package:zulip/api/model/initial_snapshot.dart';
 import 'package:zulip/api/model/model.dart';
 import 'package:zulip/api/model/narrow.dart';
+import 'package:zulip/api/route/channels.dart';
 import 'package:zulip/api/route/messages.dart';
 import 'package:zulip/model/actions.dart';
 import 'package:zulip/model/localizations.dart';
@@ -1419,6 +1420,8 @@ void main() {
     final stream = eg.stream();
     const content = 'outbox message content';
 
+    final topicInputFinder = find.byWidgetPredicate(
+      (widget) => widget is TextField && widget.controller is ComposeTopicController);
     final contentInputFinder = find.byWidgetPredicate(
       (widget) => widget is TextField && widget.controller is ComposeContentController);
 
@@ -1469,7 +1472,32 @@ void main() {
         localMessageId: store.outboxMessages.keys.single));
     });
 
-    testWidgets('failed to send message, retrieve the content to compose box', (tester) async {
+    testWidgets('in channel narrow, failed to send message, retrieve both topic and content to compose box', (tester) async {
+      await setupMessageListPage(tester,
+        narrow: ChannelNarrow(stream.streamId), streams: [stream],
+        messages: []);
+
+      connection.prepare(json: GetStreamTopicsResult(topics: []).toJson());
+      await tester.enterText(topicInputFinder, 'test topic');
+      await sendMessageAndFail(tester);
+
+      final controller = tester.state<ComposeBoxState>(find.byType(ComposeBox)).controller;
+      controller as StreamComposeBoxController;
+      await tester.enterText(topicInputFinder, 'different topic');
+      check(controller.content).text.isNotNull().isEmpty();
+
+      // Tap the message.  This should put its content back into the compose box
+      // and remove it.
+      await tester.tap(outboxMessageFinder);
+      await tester.pump();
+      check(outboxMessageFinder).findsNothing();
+      check(controller.topic).text.equals('test topic');
+      check(controller.content).text.equals('$content\n\n');
+
+      await tester.pump(kLocalEchoDebounceDuration);
+    });
+
+    testWidgets('in topic narrow, failed to send message, retrieve the content to compose box', (tester) async {
       await setupMessageListPage(tester,
         narrow: eg.topicNarrow(stream.streamId, 'topic'), streams: [stream],
         messages: []);